Showing papers on "Magnetic field published in 1968"
TL;DR: Weak alternating magnetic fields outside the human scalp, produced by alpha-rhythm currents, are demonstrated and a course distribution shows left-right symmetry for the particular averaging technique used here.
Abstract: Weak alternating magnetic fields outside the human scalp, produced by alpha-rhythm currents, are demonstrated. Subject ard magnetic detector were housed in a multilayer magnetically shielded chamber. Background magnetic noise was reduced by signal-averaging. The fields near the scalp are about 1 x 10-9 gauss (peak to peak). A course distribution shows left-right symmetry for the particular averaging technique used here.
683 citations
TL;DR: The constancy of frequency in the recently discovered pulsed radio sources can be accounted for by the rotation of a neutron star as discussed by the authors, where relativistic velocities will set up in any plasma in the surrounding magnetosphere, leading to radiation in the pattern of a rotating beacon.
Abstract: The constancy of frequency in the recently discovered pulsed radio sources can be accounted for by the rotation of a neutron star. Because of the strong magnetic fields and high rotation speeds, relativistic velocities will be set up in any plasma in the surrounding magnetosphere, leading to radiation in the pattern of a rotating beacon.
651 citations
TL;DR: The observed critical parameters indicate that a laminar flow in the core, due to the earth's precession, would have weak hydrodynamic instabilities at most, but that finite-amplitude hydromagnetic instability could lead to fully turbulent flow.
Abstract: I have proposed that the precessional torques acting on the earth can sustain a turbulent hydromagnetic flow in the molten core. A gross balance of the Coriolis force, the Lorentz force, and the precessional force in the core fluid provided estimates of the fluid velocity and the interior magnetic field characteristic of such flow. Then these numbers and a balance of the processes responsible for the decay and regeneration of the magnetic field provided an estimate of the magnetic field external to the core. This external field is in keeping with the observations, but its value is dependent upon the speculative value for the electrical conductivity of core material. The proposal that turbulent flow due to precession can occur in the core was tested in a study of nonmagnetic laboratory flows induced by the steady precession of fluid-filled rotating spheroids. It was found that these flows exhibit both small wavelike instabilities and violent finite-amplitude instability to turbulent motion above critical values of the precession rate. The observed critical parameters indicate that a laminar flow in the core, due to the earth9s precession, would have weak hydrodynamic instabilities at most, but that finite-amplitude hydromagnetic instability could lead to fully turbulent flow.
442 citations
TL;DR: In this article, the Mossbauer line shape in the presence of time-dependent electric field gradients and magnetic fields is considered, and two specific soluble stochastic models are treated: (1) a static electric field gradient with a randomly fluctuating magnetic field which takes on values $+h$ and $\ensuremath{-}h$, each directed along the axis of the field gradient, and (2) as in (1), but with the fluctuating magnet field perpendicular to the orientation of field gradient.
Abstract: The M\"ossbauer line shape in the presence of time-dependent electric field gradients and magnetic fields is considered. Two specific soluble stochastic models are treated: (1) a static electric field gradient with a randomly fluctuating magnetic field which takes on values $+h$ and $\ensuremath{-}h$, each directed along the axis of the field gradient, and (2) as in (1), but with the fluctuating magnetic field perpendicular to the axis of the field gradient. Example (2) is more complex than (1), since the fluctuating field is in this case capable of inducing transitions between the nuclear levels, while in (1) this is not possible. Specific calculations for the two cases illustrate the differences between them.
432 citations
IBM1
TL;DR: In this paper, the effect of a magnetic field tilted up to 1.3 and 4.3 degrees from the normal to the (100) Si surfaces was measured, with values between 3.25 and 2.47 for a surface electron density ranging from 1.6 to 6.
Abstract: $n$-type inverted silicon surfaces were studied to examine properties of a two-dimensional electron gas as well as those properties of silicon itself. The effect of a magnetic field tilted up to \ifmmode\pm\else\textpm\fi{}90\ifmmode^\circ\else\textdegree\fi{} from the normal to the (100) Si surfaces was measured between 1.3 and 4.2\ifmmode^\circ\else\textdegree\fi{}K and up to 90 kOe. The electric field associated with the $n$-type inversion layer quantizes the surface electrons and they behave as a two-dimensional electron gas. It was found that the oscillatory magnetoconductance, due to magnetic quantization into Landau levels, depends solely upon the normal component of the magnetic field with respect to the surface. The observed splitting due to spin appears to be determined by the total magnetic field. The parallel component of the magnetic field was found to have a negligible effect on the surface quantization. The cyclotron mass, measured from the temperature dependence of the oscillation amplitude, is equal to the transverse mass of the electron in silicon and is independent of the tilt angle. The spin splitting can be quantitatively identified at certain angles where the Landau splitting is twice that of the spin splitting. The Land\'e $g$ factor determined in this way was found to be substantially larger than 2 and decreases with the increasing surface electron density. The $g$ factor has values between 3.25 and 2.47 for a surface electron density ranging from 1\ifmmode\times\else\texttimes\fi{}${10}^{12}$ to 6\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$.
318 citations
TL;DR: In this article, a theory of low-frequency drift instabilities in a nonuniform collisionless plasma is developed for general magnetic field configurations including trapped particle effects, rather than the plane geometry which has previously received most attention.
Abstract: A theory of low‐frequency drift (universal) instabilities in a nonuniform collisionless plasma is developed for general magnetic field configurations including trapped particle effects, rather than the plane geometry which has previously received most attention. A type of energy principle shows that the special equilibrium distribution F(∈, μ), of interest in minimum‐B mirror configurations, is absolutely stable to these modes provided ∂F/∂∈ < 0 together with a second condition on ∂F/∂μ. For equilibrium distributions not of this special form, in particular for a Maxwell distribution with a density gradient, the case of axisymmetric toroidal configurations with closed poloidal field lines is considered in detail. Three unstable drift modes are found, a flute‐like mode, a drift‐ballooning mode local to the region of unfavorable curvature, and a drift‐universal mode. Stability criteria and growth rates for the modes are given. The equations also describe a recently discussed low‐frequency trapped‐particle in...
312 citations
TL;DR: In this article, the quantum field theory of particles with both electric and magnetic charges is developed as an obvious extension of Schwinger's quantum field theories of particles having either electric or magnetic charge.
Abstract: The quantum field theory of particles with both electric and magnetic charges is developed as an obvious extension of Schwinger's quantum field theory of particles with either electric or magnetic charge. Two new results immediately follow. The first is the chiral equivalence theorem which states the unitary equivalence of the Hamiltonians describing the system of particles with electric and magnetic charges ${e}_{n}$, ${g}_{n}$ and the system with charges ${{e}_{n}}^{\ensuremath{'}}=cos\ensuremath{\theta}$, ${e}_{n}+sin\ensuremath{\theta}{g}_{n}$, ${{g}_{n}}^{\ensuremath{'}}=\ensuremath{-}sin\ensuremath{\theta}{e}_{n}+cos\ensuremath{\theta}{g}_{n}$. This result holds in particular in the absence of physical magnetic charges. The second result is that if physical magnetic charges do occur, then, in consequence of chiral equivalence, the charge quantization condition applies, not to the separate products ${e}_{m}{g}_{n}$, but to the combinations ${e}_{m}{g}_{n}\ensuremath{-}{g}_{m}{e}_{n}$, which must be integral multiples of $4\ensuremath{\pi}$. The general solution of this condition leads to the introduction of a second elementary quantum of electric charge ${e}_{2}$, the electric charge on the Dirac monopole, besides the first elementary charge ${e}_{1}$, the charge on the electron. There are no other free parameters.
307 citations
TL;DR: In this paper, a general method is presented for calculating the structural changes resulting from electric or magnetic fields acting on anisotropy of the anisotropic susceptibility of a liquid crystal.
Abstract: Electric or magnetic fields acting on the anisotropy of the electric or magnetic susceptibility exert torques within a liquid crystal which may compete with the elastic torques determining its internal structure. A general method is presented for calculating the structural changes thus produced. Two examples are given, and the field strength for the effects is estimated to be 105 V/cm or 105 G. Two experiments are suggested to test the theory.
292 citations
TL;DR: Power spectra and fluctuations of interplanetary magnetic field from Mariner 4 data for solar active and quiet days as mentioned in this paper, for both active and non-active solar active days.
Abstract: Power spectra and fluctuations of interplanetary magnetic field from Mariner 4 data for solar active and quiet days
275 citations
TL;DR: In this paper, a gravimeter is constructed which uses the near perfect stability of superconducting persistent currents to make it a device with exceptional stability, and it is used to measure changes in the vertical position of the sphere or as changes in a feedback force, independent of the primary supporting force, which holds the sphere in a fixed position.
Abstract: A gravimeter is constructed which uses the near perfect stability of superconducting persistent currents to make it a device with exceptional stability. A superconducting sphere is levitated in the magnetic field generated by two superconducting coils. Changes in gravitational or inertial forces in the vertical direction are measured as changes in the vertical position of the sphere or as changes in a feedback force, independent of the primary supporting force, which holds the sphere in a fixed position. In its present state of development the instrument produces data which, when compared to calculated earth tides, set an upper limit on the drift rate of ±6 parts in 109 of g/day. Several possible sources of drift are discussed.
266 citations
TL;DR: In this paper, a detailed theory of electronic surface quantum states in a low magnetic field, as well as their effects on the microwave surface impedance is presented, and a considerable amount of quantitative information can be extracted from the experimental data.
Abstract: We present here a detailed theory of electronic surface quantum states in a low magnetic field, as well as of their effects on the microwave surface impedance. A marked oscillatory structure in the microwave absorption as a function of magnetic field has been carefully observed by Khaikin and by Koch et al. The quantized magnetic surface levels are bound states of electrons trapped against the surface by the magnetic field. Even though these levels are somewhat analogous to Landau levels, they have considerably different properties. Resonant transitions between these levels give rise to a series of spectral lines in the surface impedance, just as cyclotron resonance is a result of transitions between Landau levels. The present effect is essentially quantum in nature, however. A considerable amount of quantitative information can be extracted from the experimental data. The Fermi velocity, radius of curvature of the Fermi surface, and mean free time at certain points on the Fermi surface can be obtained. Most novel, however, is the fact that one can extract information on the scattering of electrons by the surface, as a function of impact angle.
TL;DR: In this paper, a detailed study of the velocity, intensity and magnetic-field fine structure in and around a sunspot is described, where the magnetic field in these knots causes a striking decrease of the line depth.
Abstract: The observational set-up for a detailed study of the velocity, intensity and magnetic-field fine structure in and around a sunspot is described. On highly resolved spectra we detected in the vicinity of a sunspot a large number of points with strong magnetic fields (magnetic knots). The magnetic field in these knots causes a striking decrease of the line depth (or a ‘line gap’ after Sheeley, 1967). The properties of the magnetic knots are: (1) magnetic fields up to 1400 gauss; (2) diameter ≈ 1100 km; (3) coincidence with dark intergranular spaces; (4) generally downward material motion; (5) lifetime>30min; (6) estimated total number around an unipolar spot ⩾ 2000; (7) combined magnetic flux comparable to the sunspot flux; (8) coincidence with Ca+ plages. For the smallest sunspots (pores) we obtained magnetic fields >1500 gauss. Hence a magnetic field of about 1400–1500 gauss appears to be a rather critical level for pore and spot formation. We found a large number of small areas producing line gaps without measurable magnetic field. These ‘non-magnetic gap-regions’ coincide with bright continuum structures. Some aspects arising from the occurrence of hundreds of magnetic knots in an active region are discussed in the last section.
TL;DR: Magnetic field lines of force random walk and astrophysical magnetic fields random fluctuations, noting interplanetary magnetic field and solar photosphere turbulence are noted in this article, where the authors discuss the effects of magnetic field line of forces random walk on magnetic field random fluctuations.
Abstract: Magnetic field lines of force random walk and astrophysical magnetic fields random fluctuations, noting interplanetary magnetic field and solar photosphere turbulence
TL;DR: Magnetic field configuration in outer magnetosphere from data obtained by Interplanetary Monitoring Platform /IMP/ was analyzed by as discussed by the authors, where the magnetic field configuration was determined from data collected from the outer magnetosphere of the Earth's magnetosphere.
Abstract: Magnetic field configuration in outer magnetosphere from data obtained by Interplanetary Monitoring Platform /IMP/
TL;DR: In this article, the authors consider the effects of heating when the applied field is changed suddenly and magnetic flux enters adiabatically into the bulk of a semi-infinite slab of superconductor.
Abstract: The isothermal critical‐state model of hard superconductors is extended to include the effects of heating when the applied field is changed suddenly and magnetic flux enters adiabatically into the bulk. We consider the following specific situation. A semi‐infinite slab of superconductor is cooled in a magnetic field lying in its surface plane. Next, the external field is raised isothermally by an amount Hs. This excess field decreases linearly to a depth δ= 10Hs/4πJc from the surface. Finally, the field is raised by an infinitesimal amount ΔH in a time short compared to the thermal diffusion time and long compared to the electromagnetic diffusion time. Each element of volume exposed to the changing field receives a thermal impulse proportional to the local‐flux‐change times Jc. This thermal impulse, in turn, lowers the critical current and allows more flux to penetrate. We find that if Hs exceeds some critical value Hfj, then the isothermal critical state is not the only allowed state of the superconductor. This instability field is given in terms of the critical current density Jc, derivative of the critical current density with temperature, ∂Jc/∂T, and the volume specific heat C by the formula Hfj= [−π3CJc/(∂Jc/∂T)]1/2. The application of the incremental field ΔH can initiate an avalanching process, or a flux jump, that terminates in an adiabatic critical state. Immediately following the flux jump the internal field, the induced supercurrent, and the temperature rise at each position are associated in a self‐consistent way with the avalanche of flux that has entered the superconductor. In this framework a flux jump is viewed as a switching from the isothermal critical state to an adiabatic critical state. The magnitude of the jump is related to Js and is calculated.
TL;DR: In this paper, the spin wave contribution to low temperature magnetization is considered in the limits of strong and very weak ferromagnetism, and a simple equation for the magnetic isotherms is obtained in this limit and shown to be valid over a wide temperature range.
Abstract: Calculations are given for the dependence on temperature and magnetic field strength H of the magnetization M of ferromagnetic metals treated on the basis of the itinerant electron model. The spin wave contribution to the low temperature magnetization is considered in the limits of strong and very weak ferromagnetism. For the first limit, problems related to the well-known divergence of the zero field differential susceptibility are briefly discussed. The main part of the paper is concerned with the single particle contributions to the magnetization and associated differential susceptibility for very weak ferromagnetism. A simple equation for the magnetic isotherms is obtained in this limit and shown to be valid over a wide temperature range including 0 °K and the Curie temperature. This equation implies that plots of M 2 against H / M at various temperatures in this range give a series of parallel straight lines. Recently measured isotherms for the material ZrZn 2 are analysed on the basis of the theory, and several characteristic properties of this material are obtained from the analysis.
TL;DR: In this article, a linearized analysis of the mechanism is given that differs from earlier treatments in several respects and is more directly applicable to the ionosphere than to laboratory plasmas.
Abstract: This paper examines the relevance to the ionosphere of a certain plasma instability mechanism previously discussed by several authors. A linearized analysis of the mechanism is given that differs from earlier treatments in several respects and is more directly applicable to the ionosphere than to laboratory plasmas. It is found that the dynamo region of the ionosphere is likely to be unstable against the growth of irregularities in electron concentration with scale sizes in the range from a few tens of meters to a few kilometers, given the presence of steady electric fields comparable to those expected to be present from tidal dynamo action. It is further suggested that the space-charge potentials associated with the growth of the dynamo-region irregularities of larger scale size can be conducted up the magnetic field lines into the F region, generating irregularities there in the presence of a vertical gradient in ionization near the equator and in the presence of horizontal gradients at high magnetic latitudes. It is shown that this theory appears to be capable of explaining many of the observed features of F-region irregularities, including their diurnal variation and their correlation with magnetic disturbance, which is in a positive sense at high latitudes and in a negative sense in the vicinity of the dip equator. The relationship of the mechanism to earlier theories of the growth of small-scale F-region irregularities is discussed.
TL;DR: In this article, the theory of nuclear spin-lattice relaxation via paramagnetic centers in diamagnetic crystals is investigated in terms of both the singlerelaxation-center and the multirelaxation center models.
Abstract: The theory of nuclear spin-lattice relaxation via paramagnetic centers in diamagnetic crystals is investigated in terms of both the single-relaxation-center and the multirelaxation-center models. In this theory, the distances between centers are allowed to be finite. A new case is found for which the theory predicts a new dependence of the spin-lattice relaxation time upon the applied magnetic field, the concentration of the paramagnetic centers, and the magnitude of the diffusion constant. An adaptation of the theory to the rotating reference frame shows that under certain conditions the spin-lattice relaxation time in the rotating frame can be larger than in the laboratory frame.
TL;DR: In this article, the propagation of cosmic rays in the regular and random interplanetary magnetic fields transferred by the clouds of the inter-planetary plasma is considered and the equation for the distribution function is obtained.
TL;DR: In this paper, an intermediate form of ion spectrum, representing neither solar wind nor magnetosheath, but characterized by an irregular envelope and occasional large flux peaks, is found to correspond to the appearance of large-amplitude (10-25 γ), irregular magnetic oscillations of 4-to 30sec period.
Abstract: Ion spectrums and magnetograms obtained simultaneously when the Vela 3A satellite crossed the earth's bow shock have been correlated. An intermediate form of ion spectrum, representing neither solar wind nor magnetosheath, but characterized by an irregular envelope and occasional large flux peaks, is found to correspond to the appearance of large-amplitude (10-25 γ), irregular magnetic oscillations of 4-to 30-sec period. The large spectral flux peaks of the shock seem to result from localized transient accelerations and decelerations of the bulk of the solar wind protons. Smaller amplitude (<5 γ), longer period (20-60 seconds), generally more regular magnetic oscillations are seen in the solar wind outside the shock where the direction of flow of ion flux peaks is found to oscillate in close correlation with magnetic waves.
TL;DR: In this paper, a densitygradient-driven collisional drift wave is identified by the dependences of ω and k on density, temperature, magnetic field, and ion mass, and by comparison with a linear theory which includes resistivity and viscosity.
Abstract: Density‐gradient‐driven collisional drift waves are identified by the dependences of ω and k on density, temperature, magnetic field, and ion mass, and by comparisons with a linear theory which includes resistivity and viscosity. Abrupt stabilization of azimuthal modes is observed when the stabilizing ion diffusion over the transverse wavelength due to the combined effects of ion Larmor radius and ion‐ion collisions (viscosity) balances the destabilizing electron‐fluid expansion over the parallel wavelength, determined by electron‐ion collisions (resistivity). The finite‐amplitude (ũ/n0 ≃ 10%) coherent oscillation, involving the entire plasma body, shows a phase difference between density and potential waves (which is predicted by linear theory for growing perturbations). The wave‐induced radial transport exceeds classical diffusion, but is below the Bohm value by an order of magnitude. Although observations have been extended to magnetic fields three times those for drift‐wave onset, turbulence has not b...
TL;DR: The position of bright knots of 30 flares at their very beginning relative to the high-resolution isogauss maps of the longitudinal component (H676∥) and maps of transverse component(H676⊥) of magnetic field were considered for seven days during the passage of the active and large spot group in September 1963 as discussed by the authors.
Abstract: The position of bright knots of 30 flares at their very beginning relative to the high-resolution isogauss maps of the longitudinal component (H
∥) and maps of the transverse component (H
⊥) of magnetic field are considered for seven days during the passage of the active and large spot group in Sept 1963 (see Table I and maps on Figures 1–8) The flare bright knots occur simultaneously in regions of opposite magnetic polarity, and the majority of these knots are adjacent to neutral line H
∥ = 0, although not coinciding precisely with this line (Figure 9) Lenticular form of flare knots and the motions of bright material of flares is restrained by transversal field H
⊥ Also flares are closely associated (83%) with so-called ‘bifurcated regions’, where specific crossing of transverse components takes place (Figures 4–5) There is well-expressed (80%) coincidence of flare knots with the strongest (positive or negative) electric currents as determined from the relation j = c/4π rot H The relation of results obtained to some existing theories of flares is briefly discussed
Journal Article•
TL;DR: In this article, a method for removing impurities from a copper electrolyte of having a free sulfuric acid concentration of less than 700g/l was proposed, and containing at least arsenic among arsenic, antimony and bismuth as impurities.
Abstract: A method for removing As, or As and Sb and/or Bi wherein acidic solution of sulfuric acid such as a copper electrolyte of having a free sulfuric acid concentration of less than 700g./l. and containing at least arsenic among arsenic, antimony and bismuth as impurities is warmed to be above 50 DEG C. or preferably above 60 DEG C. with the addition of H3AsO4 in advance as required, one or a mixture of both of Sb2O3 and Bi2O3 preferably kneaded with water or the added solution is added to and mixed with the solution and the produced precipitate is separated to discharge the impurities out of the solution.
TL;DR: The velocity distribution of photoelectrons in the energy range 7-20 ev has been investigated at altitudes near 600 km by measuring the intensity of radar Thomson scatter from the steady-state level of plasma waves in the ionospheric plasma.
Abstract: The velocity distribution of daytime ionospheric photoelectrons in the energy range 7–20 ev has been investigated at altitudes near 600 km by measuring the intensity of radar Thomson scatter from the steady-state level of plasma waves in the ionospheric plasma. This intensity depends on the velocity distribution through plasma wave-particle interactions such as Landau damping. The measurements were carried out at the Arecibo Ionospheric Observatory (L ≈ 1.5, geographic latitude 18°N). The experimental values for the vertically upward flux of photoelectrons are in the range (3–10) × 108 cm−2 sec−1, and, for the upward energy flux, (3–13) × 109 ev cm−2 sec−1. The experiments show that the daytime downward flux is equal to the upward flux to within experimental error (±50%) at Arecibo. Some December 1966 observations during the presunrise and postsunset periods have detected photoelectrons originating at the magnetic conjugate point. The effect of a weak (ωp > ωc) magnetic field on the Landau damping of plasma waves by a Maxwellian velocity distribution was investigated by changing the angle θ between the radar beam and the magnetic field. The theoretical prediction that the Landau damping is orders of magnitude larger than the field-free case and depends strongly on angle was verified experimentally.
TL;DR: Relativistic electron gas in strong magnetic field, obtaining equation of state with quantum theory as discussed by the authors, was used to obtain the Eq. 1.1.0.0
Abstract: Relativistic electron gas in strong magnetic field, obtaining equation of state with quantum theory
TL;DR: In this paper, it was shown that the electron energization was caused by the electric fields associated with some static 4-kev potential difference in the magnetosphere, which is known to exist and have been measured directly.
Abstract: Rocket-borne observations were made of a nearly monoenergetic beam of electrons in association with a prebreakup auroral display. The characteristic energy of this beam was about 4 kev and was very stable over a 150-second period of time. The nature of this energy spectra strongly suggests that the electron energization was by the electric fields associated with some static 4-kev potential difference in the magnetosphere. A model in which this potential was established directly along a magnetic field line cannot be uniquely excluded by these observations but is discounted on other grounds. The alternative is a model in which the required electric field is transverse to the magnetic field lines. Such electric fields are known to exist and have been measured directly. Energization of low-energy electrons by an electric field of this geometry, would appear to require that these electrons be stably trapped on closed lines of magnetic force, the energization occurring by virtue of gradient and line curvature drift across equipotential lines. It is this process, which is similar to that proposed by Taylor and Hones (1965), that is believed to have produced the auroral particles observed in this aurora. The electrical potential differences known to be available in the magnetosphere although sufficient to produce these 4-kev electrons are inadequate to produce the 100-kev electrons seen in association with the aurora, thus implying the existence of more than one acceleration mechanism.
TL;DR: In this paper, thermal anisotropy of electrons and instability of circularly polarized electromagnetic waves propagating along magnetic field in solar wind were investigated. But the results were limited to the case of solar wind.
Abstract: Thermal anisotropy of electrons and instability of circularly polarized electromagnetic waves propagating along magnetic field in solar wind
TL;DR: Perturbations of interplanetary magnetic field by lunar wake compared with disturbed solar plasma flow as mentioned in this paper showed that the magnetic field was perturbed by the lunar wake and solar plasma flows.
Abstract: Perturbations of interplanetary magnetic field by lunar wake compared with disturbed solar plasma flow